In a typical wax filled actuator, the wax is contained in rigid cup by an elastic diaphragm clamped at its periphery between the cup and a guide. The guide may include an elastic plug held tightly in position by the guide. A piston is received in the guide and is in contact with the plug. The temperature sensing wax material contained in the cup transfers pressure to the piston by means of the diaphragm and the plug. On cooling, the piston is returned to its original position by means of a return spring.
A variant of the diaphragm type actuator employs an incompressible fluid between the diaphragm and piston to transfer force from the wax to the piston. The incompressible fluid is contained by seals between the piston and the guide.
An alternative form of wax filled thermal actuator employs a synthetic rubber sleeve-like component shaped like the ‘finger of a glove’ which surrounds the piston. As the temperature increases, pressure from the expansion of the thermostatic material moves the piston with a lateral squeeze and a vertical push.
There is a need in the art for a compact and simplified thermal actuator that generates a pre-determined movement from a specified temperature change.
There is a need in the art for a compact and durable thermal actuator that will function over many thousands of cycles.